Voice sensing using multiple microphones

ABSTRACT

A noise cancelling headset includes an earpiece, the earpiece including a feedback microphone, a feed-forward microphone, and an output driver. A first feedback filter receives an input from at least the first feedback microphone and produces a first filtered feedback signal. A first feed-forward filter receives an input from at least the first feed-forward microphone and produces a first filtered feed-forward signal. A first summer combines the first filtered feedback signal and the first filtered feed-forward signal and produces a first output signal. An output interface provides the first output signal as an output from the headset.

PRIORITY CLAIM

This application is a continuation of, and claims priority to, U.S.patent application Ser. No. 15/728,732, filed Oct. 10, 2017, which is acontinuation of, and claims priority to, U.S. patent application Ser.No. 14/657,604, filed Mar. 13, 2015, now U.S. Pat. No. 9,905,216.

BACKGROUND

This disclosure relates to voice sensing, and in particular, using themicrophones of an active noise reduction system to detect the voice ofthe system's user.

U.S. Pat. No. 8,682,001, by Annunziato et al., incorporated here byreference, describes an in-ear active noise reduction (ANR) headset thatincludes two microphones in each earbud, one inside the acoustic systemfor providing feedback-based ANR, and one outside the acoustic systemfor providing feed-forward-based ANR. In a commercial product embodyingthat patent application, the Bose® QC® 20 Acoustic Noise Cancelling®headphones, a fifth microphone was provided, in the cable joint housingof the headphone cable, for picking up the user's voice for use incommunications applications. Other in-ear headphone products tend toalso include communications microphones somewhere in the headphonecable, rather than in the earbud, as do many on-ear and around-earheadphones.

Detecting the voice of a user of headphones is useful for at least tworeasons. First, it provides near-end audio for transmitting to acommunication partner. Second, headphones, and in particular ANRheadphones, tend to distort how the user hears his own voice whenspeaking, which we refer to as self-voice. Playing back the user's ownvoice within the headphones, which we refer to as side-tone audio,allows the user to hear his voice, and properly modulate it forconversation either with an electronic communication partner orface-to-face. Providing an accurate side-tone requires good voicedetection.

SUMMARY

In order to enable telephony or radio communication in noisyenvironments where ANR headsets are worn, a microphone that has goodnoise rejection is needed. The microphone noise rejection should besufficient to enable sufficiently-high SNR for communication partners toprovide intelligibility and comfort, and provide natural self-voice tothe user via side-tone without introducing significantly moreenvironmental noise than is present without side-tone. The standardsolution for this is to use a dipole or other gradient microphone on aboom, positioned as close to the lips as practical. However, in the caseof comfortable-to-wear in-ear headsets, suspending such a boom is achallenge. The invention provides good voice pick-up without requiring aboom. Examples of applications include headsets for use in airplanes,mobile telephony in large raucous groups, industrial communicationheadsets and tactical headsets for military use. In these applications,the voice need not sound completely natural as complete fidelity is notexpected.

In general, in one aspect, an in-ear noise cancelling headset includesfirst and second earpieces, each earpiece including a respectivefeedback microphone, a respective feed-forward microphone, and arespective output driver. A first feedback filter receives an input fromat least the first feedback microphone and produces a first filteredfeedback signal. A first feed-forward filter receives an input from atleast the first feed-forward microphone and produces a first filteredfeed-forward signal. A first summer combines the first filtered feedbacksignal and the first filtered feed-forward signal and produces a firstoutput signal. An output interface provides the first output signal asan output from the headset.

Implementations may include one or more of the following, in anycombination. A second feedback filter may receive an input from thesecond feedback microphone and produce a second filtered feedbacksignal; the first summer combines the first filtered feedback signalwith the second filtered feedback signal. A second feed-forward filtermay receives an input from the second feed-forward microphone andproduce a second filtered feed-forward signal; the first summer combinesthe first filtered feed-forward signal with the second filteredfeed-forward signal. A second summer may combine the first and secondfeedback microphone inputs and provide a summed feedback microphonesignal to the first feedback filter. A second summer may combine thefirst and second feed-forward microphone inputs and provide a summedfeed-forward microphone signal to the first feed-forward filter. Asecond feedback filter may receive an input from the second feedbackmicrophone and produce a second filtered feedback signal, while a secondfeed-forward filter receives an input from the second feed-forwardmicrophone and produces a second filtered feed-forward signal; a secondsummer combines the second filtered feedback signal with the secondfiltered feed-forward signal to produce a second output signal.

At least the first earpiece may include an additional externalmicrophone, and the first feed-forward filter may include a feed-forwardarray processing filter receiving inputs from the first or secondfeed-forward microphone and the additional external microphone,producing an array-filtered signal; the first summer combines the arrayfiltered signal with at least the first feedback filtered signal toproduce the output signal. A joint housing may be connected to cordsleading from the earpieces, the joint housing including an array ofmicrophones, and an array processing filter may receive inputs from thearray of microphones and the first and second feed-forward microphones,producing an array-filtered signal; the first summer combines the arrayfiltered signal with at least the first feedback filtered signal toproduce the output signal.

A second summer may combine the first and second feedback microphoneinputs and provide a summed feedback microphone signal to a comparator,while a third summer combines the first and second feed-forwardmicrophone inputs and provides a summed feed-forward microphone signalto the comparator, with an output of the comparator controllingoperation of the first feedback filter and the first feed-forward filterbased on a comparison of the summed feedback microphone signal with thesummed feed-forward microphone signal. The output of the comparator maydeactivate the first feedback filter when the comparison indicates thatthe summed feedback microphone signals have less signal content than thesummed feed-forward microphone signals above 500 Hz. The output of thecomparator may deactivate the first feed-forward filter when thecomparison indicates that the summed feedback microphone signals havemore signal content than the summed feed-forward microphone signalsbetween 150 Hz and 500 Hz.

In general, in one aspect, an in-ear noise cancelling headset includesan earpiece including a feedback microphone and an output driver. Afeedback loop receives a first signal from the feedback microphone andprovides an antinoise signal, based on the first signal, to the outputdriver. The feedback loop includes a feedback compensation filter thatreceives the first signal and produces the antinoise signal. Atfrequencies at which voice sounds produced by the wearer of the headsettend to be amplified within an occluded ear canal, the feedbackcompensation filter produces antinoise at levels selected to counteractsuch amplification without otherwise cancelling the voice sounds. Anoutput interface provides at least the first signal as a voicecommunication signal output from the headset.

Implementations may include one or more of the following, in anycombination. A feed-forward microphone may be coupled to space outsidethe earpiece, a feed-forward loop receiving a second signal from thefeed-forward microphone and providing a second antinoise signal based onthe second signal to the output driver, via a feed-forward compensationfilter, with a voice circuit receiving the first signal and the secondsignal, applying a filter to the second signal, and combining thefiltered second signal with the first signal to generate the voicecommunication signal. A feed-forward microphone may be coupled to spaceoutside the earpiece, a voice microphone, separate from the feed-forwardmicrophone, may also be coupled to space outside the earpiece, with afeed-forward loop receiving a second signal from the feed-forwardmicrophone and providing a second antinoise signal based on the secondsignal to the output driver, via a feed-forward compensation filter,while a voice circuit receives the first signal and a third signal fromthe voice microphone, applies a filter to the third signal, and combinesthe filtered third signal with the first signal to generate the voicecommunication signal. First and second feed-forward microphone may becoupled to space outside the earpiece, with a feed-forward loopreceiving a sum of a second signal from the first feed-forwardmicrophone and a third signal from the second feed-forward microphone,and providing a second antinoise signal based on the sum to the outputdriver, via a feed-forward compensation filter, while and a voicecircuit receives a difference of the second signal and the third signal,applies a filter to the difference, and combines the filtered differencesignal with the first signal to generate the voice communication signal.

Advantages include detecting the user's voice and providing it to thesame user or to communication partners in a clear and intelligiblemanner, without the use of an additional voice microphone, and withbetter intelligibility than prior solutions using dedicated voicemicrophones.

All examples and features mentioned above can be combined in anytechnically possible way. Other features and advantages will be apparentfrom the description and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a cross-sectional view of an in-ear active noise reducingheadphone and a portion of the head of a wearer.

FIG. 1B shows a perspective external view of a set of in-ear activenoise reducing headphones.

FIG. 2 shows a schematic view of the different paths sound takes to theear when a person speaks.

FIGS. 3 through 11 show block diagrams of signal flows in headphones.

DESCRIPTION

As shown in FIG. 1A, an active noise reduction (ANR) headphone 100includes two microphones mounted to each earbud 102. A feedbackmicrophone 104 is located inside the acoustic structure 106 of theearbud 102, and detects sound pressure inside the acoustic structure,which is very similar to the sound pressure inside the user's ear canal108, i.e., the sound the user hears. A feed-forward microphone 110 islocated outside the acoustic structure of the earbud, and detects soundpressure reaching the ear before it passes through the mechanicalstructures of the earbud. The feed-forward microphone is used in afeed-forward noise cancellation path to provide a filtered noisecancellation signal to an output transducer 112. The signals output bythe transducer 112 cancel sound that enters the ear canal. The feedbackmicrophone is used in a feedback loop to detect and cancel sound withinthe ear canal that is still present after the feed-forward cancellation,including sounds entering the ear canal from inside the head, ratherthan through the air path from outside. In some examples, only one ofthe feed-forward or feedback cancellation path is provided.

In a typical commercial implementation, such as that shown in FIG. 1B,two matching earbuds 102 a and 102 b are provided, each havingrespective feedback and feed-forward microphones and output transducerscontained within them. The two earbuds are connected via cords 120 a and120 b to a module 122. The module 122 may provide buttons 124 forcontrolling the headphones, and an additional microphone 126 for use inmaking phone calls or other voice interactions with connected devices.In some cases, the microphone 126 is of a different type from themicrophones 104 and 110 used to provide ANR in the earbuds, owing to thedifferent performance requirements of voice communication and noisereduction. In the example of FIG. 1B, the module 122 also serves as thejoint housing of the headphones, with a single cord 128 exiting toconnect to external devices, such as signal processing circuitry oraudio source circuitry (not shown). In other examples, the module 122with buttons and microphone may be separate from the joint housing,often located along one of the two cords 120 a or 120 b, or farther downthe single cord 128. In some examples, all of the processing circuitryis contained within the earbuds or in the module 122, including awireless interface for external communication, and the cord 128 toexternal devices is omitted, eliminating the primary reason to have thejoint housing. An on-ear or around-ear headphone will have the samecomponents, but generally arranged more spaciously, as their earpieceshave more room for the components, but may also provide less of a sealto the ear canal.

In many cases, neither the joint housing nor a position along one of thecords provides an ideal location for capturing a good quality voicesignal. Reasons for this include the distance from the mouth, and thevariability of that distance, the orientation of the speaker relative tothe mouth, and the variability of that, and the possibility that themicrophone may be blocked by clothing. In some examples, the cords arerouted behind the head, and simply don't go any closer to the mouth thanthe earbuds themselves.

Instead of using the microphone 126 in the module 122, the user's voicecan be identified within the signals from the feedback and feed-forwardmicrophones. Neither the feedback microphones nor the feed-forwardmicrophones provide a high-quality voice communication signal on theirown, but the separate microphone signals can be filtered and combined tocreate a single signal that accurately represents the user's voice

When a person speaks, they hear their own voice both through the air andthrough their own head. Occluding earphones block higher frequencysounds from the user's mouth from reaching the user's ear through theair path, while causing a boost in low frequency sounds passing throughthe user's head due to the occlusion effect. As a result, differentspeech sounds couple differently from their site of production to thelocations of the ANR microphones, as illustrated in FIG. 2. Voicedsounds (sounds produced by moving air through the larynx 210) couplewell through the head to a feedback microphone inside the occludingearphone as shown by arrow 202. Fricatives (sounds produced by movingair past the lips and teeth, arrow 204), also called unvoiced sounds,and other sounds coming from the mouth 212 do not couple well to thefeedback microphone.

The feed-forward microphones are exposed to both types of speech soundsthrough the air path, see arrows 204 and 206, but are not generallypositioned well to detect such sounds with an adequate sensitivity to beuseful as communication headphones on their own. The feed-forwardmicrophones can be used, however, to fill in the gaps from the feedbackmicrophones, allowing the reconstruction of a reasonably intelligiblevoice signal.

A set of feedback/feed-forward noise canceling headphones, such as theQuietComfort® 20 Acoustic Noise Canceling® headphones from Bose®Corporation, shown in FIGS. 1A, 1B, and 2, has a total of fourmicrophones available, as described above. As shown in FIG. 2, theseheadphones have an ear tip 114 that is designed to just seal theentrance of the ear canal 108, as described in U.S. Pat. No. 8,737,669,by Monahan et al., incorporated here by reference. Sealing at theentrance of the ear canal, and not more deeply, has the effect ofmaximizing the level of body-conducted voice sounds 202 in the earcanal, where the feedback microphones can detect them via the frontcavity of the earbud.

The feedback and feed-forward microphone signals can be combined inseveral ways to generate an improved voice signal.

In one example, as shown in FIG. 3, the four microphone signals are eachlinearly equalized and then mixed together to generate the voice outputsignal. The voice output signal is then provided to additionalprocessing elements, not shown, or output from the headset over a wiredor wireless interface, not shown. A separate equalization 302, 304, 306,308 may be applied to each of the four signals, and the equalizedsignals are summed 310. Other filters are used to implementfeedback-based and feed-forward-based noise cancellation, not shown. Inother examples, as shown in FIG. 4, the two feedback microphone signalsand the two feed-forward signals may each be combined 312, 314 beforeequalizations 316, 318 are applied, on the assumption that the signalsare essentially the same on both sides, while using the signals fromboth sides improves the signal-to-noise ratio by 3 dB. Equalizing thesummed signals can save resources within the circuitry.

In some examples, the equalization 302, 308, or 316 for the feedbacksignals pass predominantly lower-frequency sounds, corresponding tobody-conducted voiced sounds. The equalization 304, 306, or 318 for thefeed-forward signals pass predominantly higher-frequency sounds,corresponding to the air-conducted unvoiced sounds missing from thebody-conducted signals. In each case, the equalizations may simply applygain shaping to the microphone signals, but they may also include delayor non-minimum phase terms to ensure that the signal paths mix to besteffect, i.e., achieve the most natural voice, in order to compensate fordifferent sound speeds through the head and through the air around thehead. In another example, as shown in FIG. 5, the same topology forequalizations as in FIG. 3 is used, but the left and right sets ofmicrophones are summed independently 320, 322, to produce a binauralvoice signal. Equalization is given as the example here, but inpractice, any appropriate filtering may be applied to each of themicrophone signals. The summing can be uniform or weighted, or weightingmay be combined with the filtering stages. The discrete elements shownin the figures are for illustration only, in practice, all of theprocessing may be handled in a single device, such as a digital signalprocessor.

If more signal processing capability is available, then more can be donethan simply filtering and summing the signals. For example, in thetopology of FIG. 3, four estimates of the speech signal may begenerated, by, for example, applying noise suppression techniqueswell-known in the art to individual microphone signals and thencombining the four estimates by averaging.

The signal provided by the feed-forward microphones 110R, 110L can befurther improved as shown in FIG. 6 by adding additional externalmicrophones 324R, 324L. The signals from the feed-forward and additionalexternal microphones are combined in feed-forward array processingstages 326R, 326L to improve the signal to noise ratio (SNR, orequivalently, voice-to-noise ratio), thereby sensing the wearer's voicemore strongly than ambient noise. Each pair of microphones provides anarray, one on each side of the head, with a main lobe oriented towardsthe mouth. A first-order gradient reception pattern, such as afigure-eight pattern increases the voice-to-noise ratio due to theproximity effect. Providing an array on each side and adding thosetogether (328) further increases the voice-to-noise ratio. The left andright feedback signals are then summed 329 with the feed forward arraysignal; alternatively, the summations 328 and 329 could be combined, or,as in FIG. 4, the feedback signals may be combined before being passedthrough a single filter and then combined with the array-processedsignals.

Another approach, the topology for which is shown in FIG. 7, is to placeat least two microphones 330, 332, in the joint housing to create anend-fire array looking upward toward the wearer's mouth. The jointhousing is typically suspended or clipped near the center of thewearer's chest. The main lobe of the array should accommodate thevarying angle at which the joint housing might be clipped while stillbeing largely sensitive to the wearer's voice. An advantage of thisapproach is that the array looks upward to sense the wearer's voice,whereas the noise sources to be rejected are typically horizontallylocated around the wearer (e.g., other people). The joint housingmicrophone signals are combined and equalized 334 to produce a singlesignal. The signal from the joint housing array processing is furthercombined with the earbud feed-forward microphone signals (which maythemselves be array signals, as in FIG. 6) for array processing 336.This can further improve the SNR sensing of the air-conducted voicebefore combining it with the body-conducted signal.

In another example, as shown in FIG. 8, further improvement inspeech-to-ambient SNR and speech naturalness can be had by dynamicallyusing the relative level at the feedback and feed-forward microphones todetect when the wearer is making certain types of speech sounds. Thiscan be used to gate the feedback and feed-forward voice signal paths onand off or, more generally, change the equalization applied on aframe-by-frame (approximating a phoneme by phoneme) basis in order toachieve a more natural-sounding result. Essentially, this provides arobust voice activity detector (VAD). In the example topology of FIG. 8,the two feedback signals are combined 350, the two feed-forward signalsare combined 352, and the two combined signals are compared 354. Theresults of the comparison are provided to the equalizers 356, 358, 360,362, with the control input from the comparison 354 switching differentequalizers on or off, or changing their equalization properties. Thistechnique can be combined with any of the other signal flow topologiesabove; the topology of FIG. 3 is used for reference only.

The determination of the current speech sound may be done based onbroad-band level or, preferably, by looking at portion(s) of thespectrum. For example, a high signal level from 150-500 Hz at thefeedback microphone relative to the feed-forward microphone means avoiced sound is being made, and the feedback microphones should be used,possibly with some small contribution from the feed-forward microphones.Conversely, a high signal level above 500 Hz at the feed-forwardmicrophones relative to the feedback microphones corresponds to anunvoiced sound, and the feed-forward microphone signal is preferred.Comparing feedback with feed-forward microphone signals, rather thansimply looking at the raw signals, prevents speech processing fromtriggering when residual external sound leaks into the ear canal,reaching the feedback microphone.

In some examples, activation or modification of the differentequalization paths is extended to the frequency domain, with a binarymasking approach being used to modify each of the microphone signals ona frequency bin-by-bin basis based on a predetermined relativemagnitude/phase relationship representative of typical human speech whenthe headset is worn. See, for example, U.S. Pat. No. 8,218,783, byKatzer and Hartung, U.S. Pat. No. 8,611,554, by Short and Walters, andU.S. Pat. No. 8,767,975, by Short, all incorporated here by reference.

The system described above can also be used to improve bandwidthextension processing of the near-field voice signal. By “bandwidthextension,” we refer to artificially extending the bandwidth of a voicesignal, by synthesizing sounds in bands where there is no signal orinadequate SNR to get a good signal. Using both occluded and free-airsensors provides discrimination of voiced and unvoiced speech. Thoseinputs are then combined to produce bandwidth extension models that aremore effective than the state of the art. In addition, a combination ofother sensor types, such as accelerometers, may also yield moreeffective bandwidth extension models. Although the voice signal at thefeedback microphone is of high voice SNR due to ANR and the occlusioneffect, it lacks higher-frequency voice content. By artificiallyextending the bandwidth of voice received by the feedback microphone, afull-band, high SNR approximation of voice content can be created.Methods of bandwidth extension known in the art include harmonicextension, linear prediction, envelope estimation, and feature mapping.These and other methods can be extended by also using signals from thefull-band, lower-SNR feed-forward microphone. In one example, harmonicsare added to the feedback microphone signal such that the mean squarederror in the higher-frequency spectrum between the feed-forward andfeedback microphones is minimized. In a second example, an a-priorimodel of bandwidth extension is chosen from a codebook to minimize errorbetween the bandwidth-extended higher-frequency speech envelope of thefeedback microphone signal versus that of the feed-forward microphonesignal. In a third example, speech is characterized as either voiced orunvoiced by comparing the relative speech energy between thefeed-forward and feedback microphones, which then determines if abandwidth extension model should be applied to the feedback microphonesignal (in the case of unvoiced speech) or not (in the case of voicedspeech). In all of the above examples, use of the feed-forwardmicrophone may be limited to instances where voice is present asdetected by a voice activity detector.

With improved bandwidth extension models, the extended bandwidth cansound more realistic and/or cover a greater bandwidth. There are severalbenefits in applying bandwidth extension to near-field voice reception.Higher frequency voice content may be very hard to capture inearbud-mounted feed-forward microphones, at least with a high SNR, dueto directivity of the mouth and the microphones. While that results ineither a limiting of voice bandwidth or introduction of a low-SNR signalat higher frequencies, the signal can still be used to improve bandwidthextension into those frequencies. First, a low-pass filter is applied tothe entire signal, then a synthesized signal as discussed above isintroduced at higher frequencies. The synthesized signal has a higherSNR than the original high-frequency signals and can be equalized toproduce a pleasing spectrum. In some examples, the measured signal and abandwidth-extended signal are selectively mixed to aid speechintelligibility. Bandwidth extension is also useful in lower frequenciesif microphone SNR is poor, for example if the talker is in the presenceof significant low-frequency noise that masks lower-frequency speechcontent.

As mentioned, the earbuds 102 in FIGS. 1A, 1B, and 2 include an ear tip114 which seals the acoustic structure 106 to the ear canal 108. Thisimproves the noise reduction capabilities of the headphones by passivelypreventing exterior sound from entering the ear canal, but it also leadsto the occlusion effect. This results from both the blocking ofair-conducted sounds from the mouth, around the head, and into the ear,and the trapping of body-conducted sounds from the larynx into the earcanal. Some of the energy of body-conducted sounds is normally lost asthe sound exits the ear through the ear canal. Trapping the bodyconducted sound, which tends to be at the lower-frequency end of thevoice spectrum, inside the ear canal provides a bass boost to the user'svoice. Meanwhile, the air-conducted sound tends to be at the higherfrequency range, so blocking that path cuts the higher end of the user'svoice, further distorting how the user hears his own voice. This is thesource of the difference in signal content between the feedback andfeed-forward microphones, used above to reconstruct the voice signal,but it also causes the user's voice to sound unnatural to the userhimself

If desired, the feed-forward signal path filters can be adjusted toallow the user's voice to pass through the feed-forward noisecancellation path, so that the user still hears the air-conductedportion of his voice. Similarly, the feedback path can also be altered,to reduce those parts of the user's voice that are amplified within theear canal when the entrance to the ear canal is plugged by theheadphone, so that the total voice sound detected by the eardrum soundscorrect. Such techniques are described in U.S. Pat. No. 8,798,283, byGauger et al., incorporated here by reference.

Adjusting the noise cancellation paths to allow the user to hear his ownvoice may be sufficient, depending on the capabilities of the ANRcircuitry, to provide natural-sounding self-voice for the user. Theresidual voice signal in the ear canal, as detected by the feedbackmicrophone, can also be used as an output voice signal for use incommunications, as a supplement to or in place of the techniquesdescribed above. When a far-end user's voice is reproduced by theheadphone's speaker, it is detected by the feedback microphone, andwould be sent back to the far-end user as if it were the local user'svoice, so an echo is possible at the far end, but this can be resolvedusing conventional echo cancellation techniques to remove the far-endsignal from the near-end voice signal based on the known transferfunction of the in-ear system.

In some cases, it has been found that adjusting the feedback path tocancel the effects of occlusion, while providing feed-forward noisecancellation of ambient sounds, can provide a natural self-voiceexperience. The partial cancelation of the body-conducted voice,provided by the feedback noise reduction, improves self-voice perceptionenough that the loss of higher-frequency air-conducted voice componentsdue to the feed-forward noise reduction is not distracting, leaving apleasing residual voice signal in the ear canal, without unwantedoutside noise. It happens that this residual voice signal, detected bythe feedback microphone, is also good for outbound voice communication,especially when supplemented by the higher-frequency voice componentsdetected by the feed-forward microphones.

A system providing both of these features is shown in FIG. 9. Thefeedback microphones 104R and 104L provide an input to correspondingfeedback compensation filters 402 and 404, which provide a feedbackantinoise signal to the output drivers 112R and 112L. The feed-forwardmicrophones 110R and 110L provide input to the feed-forward filters 408and 410, which provide feed-forward antinoise to the output drivers(this is the same system that would be used to provide noisecancellation for the user in each of the systems shown above). The twotypes of antinoise may be summed at different points in the systemtopology, and combined with incoming voice signals (not shown), asdescribed in U.S. Pat. No. 8,073,150, by Joho and Carreras, incorporatedhere by reference. The connection to the driver is merely representativeof the ultimate signal flow.

The feed-forward microphone signals are also filtered by filters 412 and414 to provide the components of air-conducted voice that are missingfrom the residual voice detected by the feedback microphones. Thesefiltered feed-forward signals are combined with the signals from thefeedback microphones at the summation node 416. This configuration canbe combined with the various topologies described above, e.g.,corresponding microphones may be summed before being filtered, and onlya single feed-forward and/or feedback filter used for both ears and/orfor the outbound voice. In some examples, the feed-forward microphonesignals can be used during moments of quiet to adaptively tune thefeedback loop to better capture the user's voice with the feedbackmicrophones.

In other examples, as shown in FIG. 10, this method of using thefeedback microphone as a primary microphone for outbound voice iscombined with a conventional, directional voice microphone 420, insteadof the omnidirectional feed-forward noise-cancellation microphones 110R,110L, to provide the missing high-frequency content of the user's voicewithout picking up surrounding noise. The voice filter 422 may be thesame as the filter 412 used when the feed-forward microphones providethe voice content, or it may be slightly different.

In yet another example, as shown in FIG. 11, a second omnidirectionalmicrophone 424 is added to at least one side, and the pair offeed-forward microphones on that (or each) side are summed to produce aninput for the antinoise filter 408, and subtracted from each other toform a two-microphone directional array to provide input to the voicefilter 428 to isolate the desired voice content. The same arrangementmay be repeated on the other side, with a fourth omnidirectionalmicrophone 426 being summed with the left feed-forward microphone 110Las input to the left feed-forward filter 410 and subtracted to create adirectional microphone input to the second voice filter 430.

Embodiments of the systems and methods described above may comprisecomputer components and computer-implemented steps that will be apparentto those skilled in the art. For example, it should be understood by oneof skill in the art that the signal-processor-implemented steps may bestored as computer-executable instructions on a computer-readable mediumsuch as, for example, floppy disks, hard disks, optical disks, FlashROMS, nonvolatile ROM, and RAM. Furthermore, it should be understood byone of skill in the art that the signal-processor-executableinstructions may be executed on a variety of processors such as, forexample, microprocessors, digital signal processors, gate arrays, etc.For ease of exposition, not every step or element of the systems andmethods described above is described herein as part of a computerizedsystem, but those skilled in the art will recognize that each step orelement may have a corresponding computer system or software component.Such computer system and/or software components are therefore enabled bydescribing their corresponding steps or elements (that is, theirfunctionality), and are within the scope of the disclosure.

A number of implementations have been described. Nevertheless, it willbe understood that additional modifications may be made withoutdeparting from the scope of the inventive concepts described herein,and, accordingly, other embodiments are within the scope of thefollowing claims.

What is claimed is:
 1. A noise cancelling headset comprising: a firstfeed-forward microphone; a second feed-forward microphone; a firstfeedback microphone; a second feedback microphone; a first output driverconfigured to receive a first antinoise signal based on a combination ofinput from the first feed-forward microphone and the first feedbackmicrophone; and a second output driver configured to receive a secondantinoise signal based on a combination of input from the secondfeed-forward microphone and the second feedback microphone; wherein avoice signal of a user of the headset is generated using input from thefirst feedback microphone, the second feedback microphone, the firstfeed-forward microphone, and the second feed-forward microphone.
 2. Theheadset of claim 1, wherein the voice signal of the user of the headsetis generated by equalizing and then mixing together the input from thefirst feedback microphone, the second feedback microphone, the firstfeed-forward microphone, and the second feed-forward microphone.
 3. Theheadset of claim 2, wherein equalizing the input from the first andsecond feedback microphones includes passing predominantlylower-frequency sounds corresponding to body-conducted voiced sounds. 4.The headset of claim 3, wherein equalizing the input from the first andsecond feed-forward microphones includes passing predominantlyhigher-frequency sounds corresponding to air-conducted unvoiced soundsmissing from the body-conducted voice sounds.
 5. The headset of claim 1,wherein the voice signal of the user of the headset is generated bycombining and then equalizing the input from the first feedbackmicrophone and the second feedback microphone, and by combining and thenequalizing the input from the first feed-forward microphone and thesecond feed-forward microphone.
 6. The headset of claim 1, wherein thevoice signal of the user of the headset is generated by producing abinaural voice signal, the binaural voice signal produced by combiningthe first feedback microphone with the first feed-forward microphone andby combining the second feedback microphone with the second feed-forwardmicrophone.
 7. The headset of claim 1, wherein the voice signal of theuser of the headset is generated by applying noise suppressiontechniques to and then combining the input from the first feedbackmicrophone, the second feedback microphone, the first feed-forwardmicrophone, and the second feed-forward microphone.
 8. The headset ofclaim 1, wherein the voice signal of the user of the headset isgenerated by further using input from additional external microphones.9. The headset of claim 8, wherein the input from the first and secondfeed-forward microphones and the input from the additional externalmicrophones are combined using array processing to improve a relatedsignal-to-noise ratio and/or a related voice-to-noise ratio.
 10. Theheadset of claim 1, wherein the voice signal of the user of the headsetis generated by comparing combined input from the first feedbackmicrophone and the second feedback microphone with combined input fromthe first feed-forward microphone and the second feed-forwardmicrophone.
 11. A method of generating a voice signal of a user of anoise cancelling headset that includes a first feed-forward microphone,a second feed-forward microphone, a first feedback microphone, and asecond feedback microphone, the method comprising: receiving, at a firstoutput driver, a first antinoise signal based on a combination of inputfrom the first feed-forward microphone and the first feedbackmicrophone; and receiving, at a second output driver, a second antinoisesignal based on a combination of input from the second feed-forwardmicrophone and the second feedback microphone; generating a voice signalof a user of the headset using input from the first feedback microphone,the second feedback microphone, the first feed-forward microphone, andthe second feed-forward microphone.
 12. The method of claim 11, whereingenerating the voice signal of the user of the headset includesequalizing and then mixing together the input from the first feedbackmicrophone, the second feedback microphone, the first feed-forwardmicrophone, and the second feed-forward microphone.
 13. The method ofclaim 12, wherein equalizing the input from the first and secondfeedback microphones includes passing predominantly lower-frequencysounds corresponding to body-conducted voiced sounds.
 14. The method ofclaim 13, wherein equalizing the input from the first and secondfeed-forward microphones includes passing predominantly higher-frequencysounds corresponding to air-conducted unvoiced sounds missing from thebody-conducted voice sounds.
 15. The method of claim 11, whereingenerating the voice signal of the user of the headset includescombining and then equalizing the input from the first feedbackmicrophone and the second feedback microphone, and by combining and thenequalizing the input from the first feed-forward microphone and thesecond feed-forward microphone.
 16. The method of claim 11, whereingenerating the voice signal of the user of the headset includesproducing a binaural voice signal, the binaural voice signal produced bycombining the first feedback microphone with the first feed-forwardmicrophone and by combining the second feedback microphone with thesecond feed-forward microphone.
 17. The method of claim 11, whereingenerating the voice signal of the user of the headset includes applyingnoise suppression techniques to and then combining the input from thefirst feedback microphone, the second feedback microphone, the firstfeed-forward microphone, and the second feed-forward microphone.
 18. Themethod of claim 11, wherein generating the voice signal of the user ofthe headset further includes using input from additional externalmicrophones.
 19. The method of claim 18, wherein the input from thefirst and second feed-forward microphones and the input from theadditional external microphones are combined using array processing toimprove a related signal-to-noise ratio and/or a related voice-to-noiseratio.
 20. The method of claim 11, wherein generating the voice signalof the user of the headset includes comparing combined input from thefirst feedback microphone and the second feedback microphone withcombined input from the first feed-forward microphone and the secondfeed-forward microphone.